Water-soluble polymers which have the property of imparting wet-strength to paper are important specialties of the paper-making art. Certain of these polymers, which may be anionic or cationic, develop their wet strength only under acidic conditions. See U.S. Pat. Nos. 2,345,543; 2,582,840 and 2,594,014. Detrimental results of the acidic conditions are that the papermaking equipment is subjected to corrosive conditions and that the paper undergoes premature embrittlement.
Water-soluble, glyoxalated, acrylamide polymer wet strength agents are disclosed in Coscia, U.S. Pat. No. 3,556,932, incorporated herein by reference. These wet-strength agents are made from polymers with molecular weights ranging from less than about 1,000,000, preferably less than about 25,000. The polymers are reacted with glyoxal in a dilute, aqueous solution to impart --CONHCHOHCHO functionalities onto the polymer and to increase the molecular weight of the polymer through glyoxal cross-links. Low molecular weight polymers and dilute solutions are required to impart at least a 6 percent --CONHCHOHCHO functionality to the polymers without infinitely cross-linking, or gelling, them, in which condition the polymers are useless for wet-strength applications. Even at these low solids concentrations (dilute conditions), cross-linking continues and limits the shelf life of the product. For example, commercial products, supplied as 10% solid solutions, gel within about 8 days at room temperature.